ISIS militants set fire to three oil wells west of the city of Kirkuk, one of two areas of Iraq still under the terror group's control, officials said Monday.

Iraqi security forces were using bulldozers to control the fires started by the militants in the early hours of Saturday. The blazes began as an attempt to slow the advance of U.S.-backed Iraqi forces and militia groups, according to Reuters.

A member of the Oil Police Force is seen at Nahran Umran field north of Basra, Iraq, Sept. 8, 2017.
(Reuters)

The Allas oilfield, 20 miles south of Hawija, was one of the main sources of revenue for ISIS, which declared a caliphate in 2014 in parts of Syria and Iraq.

“Terrorists are trying to use the rising smoke to avert air strikes while retreating from the area towards Hawija,” army Col. Mohammed al-Jabouri told Reuters.